The present invention relates to rolling bearings which are used in environments where there is danger of water becoming mixed with the bearing lubricant. For example, this pertains to the roll neck bearings of the work rolls and backup rolls of rolling mills for steel material, guide roll bearings of continuous casting equipment for steel material, water pump bearings for automobile engines, drier roll bearings for paper-making machinery, and bearings for automobile wheels. In particular, it relates to rolling bearings endowed with superior durable life even when water seeps into the bearing.
In general, the durable life of rolling bearings decreases as moisture becomes mixed with the lubricant. For example, even when only 100 ppm of water becomes mixed with the lubricant, it is known that durable life declines by 32-48% (reference literature: Schatzberg, P. and Felsen, I. M.: Effects of water and oxygen during rolling contact lubrication, Wear, 12 (1968), pp. 331-342; and Schatzberg, P. and Felsen, I. M.: Influence of water on fatigue failure location and surface alteration during rolling-contact lubrication, Journal of Lubrication Technology, ASME Trans. F,91,2 (1969), pp. 301-307).
Accordingly, with bearings which are used in humid environments where they contact water such as roll neck bearings for rolling mills, water pump bearings, etc., conventionally, sealing countermeasures is implemented to prevent the infiltration of water into the lubricant in order to prevent any decline in durable life.
As examples of such countermeasures, there are contact and non-contact seal structures described in Japanese Patent Publication No. 55-22648, Japanese Patent Unexamined Publication No. 59-223103, etc. which disclose sealing methods for the roll neck bearings of rolling mills.
With regard to bearings which adopt the aforementioned sealing countermeasures, although sealability is improved compared to bearings which do not adopt them, and although these countermeasures help to prevent the grease (lubricant) from washing away, they are insufficient as protective measures for bearing durable life under humid environmental conditions.
That is, with regard to bearings possessing the contact seal configuration, when the temperature of the bearing declines, the air inside the bearing contracts, external moisture is absorbed into the bearing, and water becomes mixed with the lubricant. With regard to bearings possessing the non-contact seal configuration, there is a problem that water infiltrates through the crevices of the seal, and becomes mixed with the lubricant.
As stated above, since durable life is reduced by 32-48% even when only 100 ppm of moisture becomes mixed with the lubricant, there is no sealing effect relative to durable life unless the infiltration of water is completely prevented.
Conventionally, it has been unclear why water so greatly reduces the life of rolling bearings (for example, see literature: Ioannides, E. and Jacobson, B.: Dirty lubricants-reduced bearing life, Ball Bearing Journal, special '89 (1989), pp. 22-27). Consequently, there have been no life extending measures other than sealing countermeasures, and the conventional main countermeasures have exclusively been to prevent the infiltration of water by the aforementioned improvements in seal performance, but sufficiently effective countermeasures have not been obtainable.